Compounded rubber stock



Patented Jan. 9, 1951 COMPOUNDED RUBBER STGCK Alphonse Pechukas, Akron, ()hio, assignor t littsburgh Plate Glass Gompany, Allegheny County, Pa, a corporation ef Pennsylvania No-Drawing. Application July 30, 19.46,

1 Serial r-No. 687,224

16. Claims. (C1.260-33. 4)

The present invention relates to compounded rubber stocks and more particularly to rubber stocks which contain pigmentary hydrated cal cium silicate as the primary filler and reinforcingagent.

Finely divided hydrated calcium silicatehas found general acceptance as a compounding pigment not only for natural rubber .but also for those synthetic elastomeric compositions which have come to prominence in the past few years. The industry has established standards for pigmentary hydrated calcium silicate, which has been determined to impart optimum physical properties to rubberdstocks compounded therewith. For example, the hydrated calcium silicate should have an average uu'ltimate particle size of less than one micronand preferably not substantially in excess of 0.5 micron. Again the molecular ratio of lSiOz to CaO in the .calcium silicate should be not less than 2 and preferably should be above 3. In a'particular-ly effective pigment, this molecular ratio is 3.3. Hydrated calcium silicate failing to meet the expressed standards can and has been usedinrcompounded rubber'stocks. In :such instances; however, the final products will not be the full equivalents of "products compounded with hydrated calcium silicate possessing the specified properties.

' Pigmentary hydrated calcium silicate :is 'customarily prepared by precipitation from an aqueous solution of a soluble calcium salt, such :as calcium chloride, on interaction therewith of a-suitablasolublealkalimetal silicate. For

example, the introduction of a sodium silicate solution, containing about 100 grams of SiOz per liter,.into a concentrated solutionof calcium .chloride containing not less than .50 grams and preferably not less than 75; grams of the calcium chloride per liter, with vigorous agitation forms a suitable product. Other concentrations of reactants and modifications in proceduralndetails will also enable the formation of a satisfactory pigment. The precipitated calcium silicate may be recovered by decantation or filtration and is dried at a temperature sufiiciently high to remove any water which would otherwise be driven off during vulcanization, for example, about 150 C. or above. The dried product is very white and has an average particle size of less than 1 micron.

"In many respects'this finely divided hydrated calcium silicate has proven superior to other non-black pigments. When admixed with rub- "ber stocks'in relatively largepercentages, there 2 will be produced compositions which yield stifi tough, :hard vuleanizates possessing excellent abrasion resistance. vulcanizates of rubber stocks containing smaller amounts of thehy-idrated calcium silicate are characterized by'gQod tear resistance as. well as excellent heat and age ing resittance. However, *vulcanizates of synthetic elastomers, which have been compounded with large quantities of hydrated calciumsilicate to afford vmaXimum reinforcing properties therein, exhibit unsatisfactory hysteresis prop7 erties, ascharacterizedby the heat build-up: un der dynamic tension. uNatural rubber stocks containing hydrated calcium silicate frequently require longer curing times for adequate vulcanization than do natural rubber stocks proc- ---essed -with other pigmentary materials.

The efiect of hydrated calcium silicate as an ingredient of compounded synthetic elastomeric stocks is readily demonstrated in connection with vulcanizates of GR.S, a synthetic rubber which is a copolymer containing 75% of butadiene-1,3 of styrene. Stocks of the following compositions were prepared and mixed by blending the several ingredients on a roll mill in-a "conventional manner:

Rubber Stock 1 2 3 QR-S 100.0 100.0 100.0 "Zinc Oxide 5.0 5.0 5.0

Pine Tar. 5. 0 Coal Tar Softener... 5.0 Light Processing Oil 5.0 5. 0 Su1fu1 3.0 3. 5 3.5 N-Cyclo-hcxyl-iZ-benmthiozole sulfonamide.-. 1. 0 Lead Dithiiclrbamatc 1. 3 1. 3 Phenyl-beta-niphth larnina 1. 0 1.0 1. 0 Hydrated calcium silicate 66. 9 66. 9 89. 2

In. these stocks, the amounts of the several ingredients are given as parts by weight. In stocks 1 and 2, the hydrated calcium silicate represents 30 volumes per 100 volumes of GR-S, while in stock 3, the hydrated calcium silicate constitutes 40 volumes per 100 volumes of CTR- S.

Test vulcanizates nof these stocks were pro-' duced bycuring at.;280$ F. for .varying :lengthspf time. The heat build-up in the vulcanizates was determined on a Goodrich-lfiexometermvith an initial temperature of "F., a load of 1'75 pounds per square inch, and a stroke of 0.175 of an inch. The results of the tests are given in the following table, the heat bui1d-upbeing reported as'degrees rise in temperature above 100F.

Table I Stock 1, Minutes Cure at 280 F.

Stock 2, Minutes Cure at 280 F.

Stock 3, Minutes Cure F Minutes of Flexmg at 280 The tabulated results indicate clearly the extra-ordinarily high heat build-up in a vulcanizate of a synthetic elastomer which has been compounded with hydrated calcium silicate. Similar effects have been noted in vulcanizates of other forced rubber stock which exhibits generally benefited physical properties.

Other objects and advantages of my invention will become apparent from consideration of the following detailed description of certain preferred embodiments thereof.

I have found, and the present invention is based upon the discovery, that the admixture of small amounts of an alcohol with rubber stocks compounded with pigmentary hydrated calcium silicate produces compositions which yield vulcanizates having high moduli of elasticity, tensile strengths and hardness properties, as Well as improved hysteresis properties.

In practicing the invention, rubber stocks are prepared in the customary manner by blending the several ingredients including hydrated calcium silicate upon a roll mill. Immediately prior to the removal of the compounded stock from the y th elastomers c p u with hydrated 2o mill, from 2 to by Weight of an alcohol, based calcium silicate. upon the amount of hydrated calcium silicate in The utility of these vulcamzates 1s limlted, for th st ck, is added thereto and incorporated the hi h h a u p precludes then use In any therewith. In order to demonstrate the advanapp where y would be SubJeCt t0 P tages of the invention a number of batches of l n y a ic fl n A hmltatlon f bins rubber stock 2, hereinbefore identified, were prechar restricting the appllcablllty of pared embodying various alcohols as additives. thetic elastomers compounded Wlth yd a Test vulcanizates of these compositions were cium silicate, is most undesirable, In an endeavor produced by curing at 280 F. for varying lengths to obviate or at least to reduce the eat bu dp, of time. These vulcanizates were tested accordor otherwise t improve the hysteresls propertles ing to A. S. T. M. standard methods. The heat of these vulcanizates, modifications of the sulfurbuild-up in the vulcanizates was again deteraccelerator ratios Were attempted. These modlmined on a Goodrich flexometer operating for 20 fications were not successful for they were accomminutes on each sample under those conditions panied by undesirable changes in other physical previously set forth. The results of the tests are properties of the vulcamzates. S1m1larly, the given in the following table:

Table II Per Cent Minutes 1 Shore Heat Modulus Tensile Elonga- Stock 2+Add1t1ve Cureat Hard- Build- 5 F at 300% at Break iligorraeg mess up 490 53 60 624 1, 276 530 62 151 no 132 is .21 1 44 ,0 750 4.2% Octy1 1 0 293 1, 375 665 55 147 90 13s 15 241 978 690 50 5.2% 2 (Z-butoxy ethoxy) 30 312 1, 262 676 5a ethanol 425 1, 390 560 57 109 o 97 15 539 1,064 485 59 11 1, a as a 21 90 1, 141 1, 418 325 71 81 15 6 0 1,276 525 62 Ethylene GIYCOL 28 t; 211i tii 3%? 3% "57 90 1,375 1, 531 345 76 7s 15 537 1, 503 460 65 7 as as 1212 :3

99 1, 375 1, 446 320 72 76 15 411 1,446 645 59 2 5% Pro ylene GlycoL- g8 $32 Z3 22?) 3 90 a a 4'5 3% Glycerol 60 1, 07s 1, 361 30 90 1,191 1. 461 355 as addition of plasticizing agents or compatible resinous materials was found to have deleterious eifects upon the physical properties of the vulcanizates other than the heat build-up.

A principal object of my invention, therefore, is to provide an improved hydrated calcium silicate reinforced rubber stock which has acceptable hysteresis properties.

A second object of my invention is the provision of an improved hydrated calcium silicate rein- In this table the moduli and tensiles are reported as pounds per square inch. The Shore hardness was determined with a Shore Type A durometer with a 2 pound dead weight load at 30 inches. The heat build-up is reported as degrees rise above F.

These data illustrate clearly that the alcohols generally have beneficial effects upon the physical properties of vulcanizates of the synthetic elastomer, GR-S. It is also indicated that the poly- Hydroxy alcohols; or I glycolsgare particularlyg ef one standard-14min; in vzhich fective asadditives to compounded syntheticweight: elastomer stock.

(.lompositionsba'sedupon"rubberstcrclrljhere 1 V 4 1 inbeforeidentified;andincluding6%.lbyweight v of ethylene glycoLbasedluponthe hydrated calg g;g l 2' i Sulfur W n. 2.0 2. 0mm slllcate content, were prepared and samples Tetramethyl Thiumm Disulfim 1. 0 1. thereof cured. at 280 F. for varymgdengthswof: Mercaptobenzothiazolm; 0.5 0; time: Thesel-vulcanizates were:testedlundenrcona ggfigfifi 1 1 s screen 50.0 50. dit ons identlcal w th those p evlously de cribed Hydmtedhomc 330R Themesults of thetest'are'g1ven 1n thef0llow- Ethylene glycol 1. ing'tab'le TdbleIII Minutes Modulus 1 Tensile-1 1 Shore Heat Cure at 300575; atBreak, g Hard- Build- 280" 1 p.-'s. 1.- 1 11.5. 1. iness up 20; 15s 1177: 74.5 51 W 1 1 a 11s as 1 l 10. 227: 1 1575 705 Stock 1+6%oetl1ylencglycol 6O 482 1021 47s 62 90. 468- 11491 4851 62 Theresults erei again S flW he pronouncedn Samples of these compositions were vulcanized improvement 1n hysteresisnpropertles 0CCaSl0I1edfi35' at, 3 f varying lengths of t m and tested by .the: inclusion of a 1 polyhydroxy alcohol in; a. compounded erubber stock containingyhydrated calcium .silicate. The tests also indicate such modification; to1 resulttin a faster: rate. of :cure. offlthe rubber: stock. The tensile. strength; in-. dicative of the extent ofcure' of the glycol containing stock afterIlO minutes-lot cure is greater? Thei tear. resistance is reported as .pounds: per. The results of the tests-are under conditions identical with those used for- The moduli and 1 the previously described tests. tensiles are reported as poundsper. square inch.

0.1 inch thickness. given in'the following table:

Table IT/ l 1 Percent Minutes Shore Modulus Tenslle Elonga I Gure-at- 1 11 1 1 Hard Tear- Q c at 300 u at Break :gggkflt nos;

it 1 3? 5 12 l 4 14 Stock- 10 440" 1,276 655 51 15" 5. 241 1,432 755 46 15 11 7. 5 255 1, 475 720 48" 14 Stock 5;..- 1O 284 1, 560 705 50 13 15 269 l, 631 680 50 10 20 312 1, 617 650 54 11 than the tensile strength of the unmodified stock after prolonged curing.

Improvements in the properties of vulcanizates.

The results illustrate. that 'the inclusion of ethylene glycol inan amount. equal to 6% by weight of the amount of. hydrated calcium silicate in a compounded GR-I stock approximately doubles .themrate of cure of that stock. The

hysteresis properties of the isobutylene-isoprenen copolymer are seemingly unafiected by the admixture therewith of hydrated calcium silicate.

In another embodiment of the invention, .illustrating the further applicability of the prin-' ciples herein involved, the following. composia tions'basedupon neoprene, a. polymer of chlorow the parts are by ogocooorooco prone, were prepared, in which the parts are by weight:

Stoc 6 7 Neoprene 100.0 100.0 Oalcined Magnesia 4. 4. 0 Zinc Ovirle 5. 0 5.0 Sodium Ace l. 0 l. 0 Phenyl-beta-naphthylamine 3. 0 3. 0 Stearic A 3.0 3.0 Petrolatum 1. 0 l. 0 Light Processing Oil. 10.0 10.0 Di-ortho-tolylguauidine salt of Dicatechol Boratequ 1. 0 1.0 Hydrated Calcium Silicate 60.0 60. 0 Ethylene Glycol 3. 0

Samples of these compositions were vulcanized at 307 F. for 120 minutes and tested. The results are given in the following table:

Table V Per cent Modulus Tensile Shore Stock at at gfi fig Hard- Tear 300% Break g Break ness These tests show the addition of of ethylene glycol to compounded neoprene increases the hardness and tear resistance of vulcanizates thereof.

Natural rubber stocks containing the following ingredients, in parts by Weight, were prepared:

Samples of these compositions were cured at 287 F. for varying lengths of time and the vulcanizates were tested as in the preceding ex- 4 i amples. The results of the tests are given in the following table:

ble polymerizable compound alone or in admix ture with one or more organic monomeric ethyle enic compound, including acrylcnitrile, isobutylene, vinyl chloride, styrene, methyl methacrylate, and the like, yield vulcanizates of improved properties when compounded stocks thereof include an alcohol. In addition, various compounding andyulcanizing ingredients generally employed for special batches, including carbon black, calcium carbonate, aluminum hydrate, accelerators, antioxidants and the like may be included in the compositions herein described. In 7 this connection, I have observed that the inclusion of an alcohol, and preferably a polyhydroxy alcohol, in a rubber stock compounded with pigments other than hydrated calcium silicate imparts certain improvement to that stock. The eifects of an alcohol addition, however, are most pronounced in those stocks compounded with hydrated calcium silicate.

The proportions of the alcohol which is incorporated with the rubber stock varies considerably depending to a large extent upon the nature of the basic rubber in the stool; and the physical properties of vulcanizates of the stock. In general, optimum results over the entire field of physical properties follow the addition of from 2 to 10% by weight of alcohol, based upon the hydrated calcium silicate content, to the compounded rubber stock. More specifically, I prefer to employ 6% by weight of the alcohoL'based upon the hydrated calcium silicate content in the compounded stocks.

Other modifications and variations will be apparent to those skilled in the art and are possible without departing from the spirit and scope Table VI Minutes Modulus Tensile Shore Stock Cur e at at 300 at tion Hard- Tear 287 F. Per Cent Break Break ness ll 20 l, 333 2, 708 535 86 39 30 l, 319 2, 496 505 86 37 It is apparent from these data that rubber vulcanizates of increased tensile strengths result from the inclusion oi ethylene glycol in the compounded rubber stocks. Similarly improvements in the hardness and tear resistance of these vulcanizates can be noted. The reported natural of my invention as defined in the appended" claims.

What I claim is:

1. A composition comprising an elastomer of butadiene and styrene, from 30 to 100% by weight decrease based on said copolymer of pigmentary hydrated 9 calcium silicate, and from 2-10% by weight based on said calcium silicate of ethylene glycol.

2. A composition comprising a copolymer of butadiene and styrene, approximately 60% by weight based on said copolymer of pigmentary hydrated calcium silicate, and about 6% by weight based on said calcium silicate of ethylene glycol.

3. A composition comprising a copolymer of butadiene and styrene, from 40 to 100% by weight based on said copolymer of pigmentary hydrated calcium silicate, and from 240% by weight based on said calcium silicate of propylene glycol.

4. A composition comprising a copolymer of butadiene and styrene, from 40 to 100% by weight based on said copolymer of pigmentary hydrated calcium silicate, and from 2-10% by weight based on said calcium silicate of glycerol.

5. A method of preparing a composition comprising a rubber of the group consisting of natural rubber and polymers of butadiene-L3, isoprene, piperylene, 2,3-dimethyl butadiene, and 2-chlorobutadiene, which comprises milling the rubber with at least 30% by weight of finely divided l1ydrated calcium silicate based on said rubber and at least 2% by weight of an alcohol based on the weight of said hydrated calcium silicate and vulcanizing the resulting composition.

6. The method as described in claim 5 in which the amount of pigmentary hydrated calcium silicate is from 30% to 100% by weight based on the rubber and the amount of alcohol is from 2 to by weight based on the pigmentary hydrated calcium silicate.

7. A composition which comprises (1) an unvulcanized rubber of the group consisting of natural rubber and polymers of butadiene-1,3, isoprene, piperylene, 2,3-dimethyl butadiene, and 2-chlcrobutadiene, (2) 30 to 100% by weight of calcium silicate based upon the Weight of said rubber, and (3) a substantial effective amount up to 10% by weight of ethylene glycol, based upon the weight of calcium silicate in the composition.

8. A composition which comprises (1) an unvulcanized rubber of the group consisting of natural rubber and polymers of butadiene-1,3, isoprene, piperylene, 2,3-dimethyl butadiene, and z-chlorobutadiene, (2) 30 to 100% by weight of calcium silicate based upon the weight of said rubber, and (3) a substantial effective amount up to 10% of a polyhydric alcohol of the group consisting of ethylene glycol, propylene glycol, di-

ethylene glycol, and glycerol, based upon the calcium silicate in the composition.

9. A composition which comprises an unvulcanized butadiene styrene copolymer, 30 to by weight of calcium silicate based upon the weight of said copolymer, and a substantial amount up to 10% by weight of a polyhydric alcohol of the group consisting of ethylene glycol, propylene glycol, diethylene glycol, and glycerol based upon the calcium silicate in the composition.

10. A vulcanizate of a composition as defined in claim 7.

11. A vulcanizate of a composition as defined in claim 8.

12. A composition as defined in claim 8 wherein the rubber is natural rubber.

13. A vulcanizate of a composition as defined in claim 12.

14. A composition comprising an unvulcanized rubber of the group consisting of natural rubber and polymers of butadiene-1,3, isoprene, piperylene, 2,3-dimethylbutadiene, and 2-chlorobutadiene, 30 to 100% by weight of calcium silicate based upon the weight of said rubber, and 2 to 10% of an alcohol based upon the calcium silicate in the composition.

15. The composition of claim 14 wherein the alcohol is a polyhydric alcohol, a member of the group consisting of ethylene glycol, propylene glycol, diethylene glycol and glycerol.

16. The vulcanizate of a composition as defined in claim 14.

ALPHONSE PECHUKAS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,015,234 Rodman Sept. 24, 1935 2,334,526 Allison Nov. 16, 1943 2,391,281 Thompson Dec. 18, 1945 2,429,439 Westfahl et al Oct. 21, 1947 2,433,849 Lathrop et al. Jan. 6, 1948 FOREIGN PATENTS Number Country Date 115,533 Australia Aug. 6, 1942 OTHER REFERENCES Industrial and Engineering Chemistry by Fisher, August 1939, pages 941942. Rubber Age, Sept. 1945, page 732. 

14. A COMPOSITION COMPRISING AN UNVULCANIZED RUBBER OF THE GROUP CONSISTING OF NUTURAL RUBBER AND POLYMERS OF BUTADINE-1,3, ISOPRENE, PIPERYLENE, 2,3-DIMETHYLBUTADINE, AND 2-CHLOROBUTADINE, 30 TO 100% BY WEIGHT OF CALCIUM SILICATE BASED UPON THE WEIGHT OF SAID RUBBER, AND 2 TO 10% OF AN ALCOHOL BASED UPON THE CALCIUM SILICATE IN THE COMPOSITION. 